Arc shield for rotary electrical switch

ABSTRACT

A molded insulating ring inserted into a rotary electrical switch deck is positioned adjacent the interior deck wall and spaced off the contact members by a plurality of pads integral with the ring. Pairs of upstanding members also integral with the ring project between adjacent stationary contacts without touching the contacts and are spaced inwardly from the deck wall to intercept carbon and metallic particles emitting from arcs occurring during switch operation. Clear areas are formed on the deck wall directly behind the upstanding members to provide a double break in the short circuit path that would normally be built up by the deposits along the wall between adjacent stationary contacts.

United States atet Robert C. Williams, III

Inventor Smithfield, N.C. Appl. No. 22,873 Filed Mar. 26, 1970 Patented June 29, I971 Assignee Gutlenllammer, lnc.

Milwaukee, Wis.

ARC SHIELD FOR ROTARY ELECTRICAL SWITCH [56] References Cited UNlTED STATES PATENTS 3,] 19.906 1/1964 Mason a ZOO/11A 3,297,836 1/1967 OMalley ZOO/11A Primary Examiner-J. R Scott Att0rneyHugh R. Rather ABSTRACT: A molded insulating ring inserted into a rotary electrical switch deck is positioned adjacent the interior deck wall and spaced off the contact members by a plurality of pads integral with the ring. Pairs of upstanding members also integral with the ring project between adjacent stationary contacts without touching the contacts and are spaced inwardly from the deck wall to intercept carbon and metallic particles emitting from arcs occurring during switch operation. Clear areas are formed on the deck wall directly behind the upstanding members to provide a double break in the short circuit path that would normally be built up by the deposits along the wall between adjacent stationary contacts.

PATENTEU .mm mm 35901741 ARC SHIELD FOR ROTARY ELECTRICAL SWETQii BACKGROUND OF THE MENTION over switches of the present designs. Direct design attempts toward improving present switches to meet either of these requirements adversely effect the ability of the switch to meet the other requirement so that switches incorporating new structural shapes and arrangements must be devised. A particular problem to be solved when switches of small size carry relatively large currents is the dispersion of arc residue so that it will not form short circuit deposits between the stationary contacts of the switch.

SUMMARY OF THE INENTION It is therefor a primary object of this invention to provide an electrical switch having an improved structure for dispersing residue formed by contact arcing during switch operation.

It is another object of this invention to provide a structure which may be readily incorporated into existing switch structures to improve the current handling capabilities of the switch by etfectively directing the residue emitted by contact arcing wherein it will not form continuous deposits along the housing walls to electrically bridge the stationary contacts.

These and other objects and advantages of this invention will become more apparent in the following specification and claims when read in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. -1 is a side elevational view of a rotary electrical switch including a switch deck containing the improved structure of this invention;

FIG. 2 is a view taken along the line 2-2 of H6. 1 exposing the bottom of the switch deck;

FIG. 3 is an enlarged view of the stator portion of the switch deck with the improved structure mounted therein;

FIG. 4 is a fragmentary view taken as indicated by the line 4-4 of FIG. 3; and

FIG. 5 is an isometric view of the particular member providing the improved structure of this invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to FIG. 1, there is shown as an example a multiposition momentary rotary switch 2 having an operating shaft 4, a position-limiting and ball detent structure designated generally by the numeral 6 and a switch deck 8 including a lower cover plate 10 held firmly against the structure 6 by a pair of nuts 12 threaded upon depending screws M. The operating shaft 4 is rotatable in either direction from a center position to any of several switch operating positions as determined by the structure 6 and is return biased to the center position by a leaf torsion spring 16 carried in an axial opening 40 in shaft 4. The upper end of spring is attached to the shaft 4 and the lower end is anchored in a cooperating rectangular opening in a plate 18 trapped between the housing and cover plate N of switch deck 8. For a more complete understanding of the ball detent position indexing and spring return features of switch 2, reference may be had to the Medicks et al. U.S. Pat. No. 3,411,375 issued Nov. 19, I968, and assigned to the assignee herein.

Referring next to FIG. 2 the switch deck 8 includes a stator comprising a molded housing 20 having a common contact ring segment 22 and a plurality of individual stationary contact segments 24 molded therein. Also included in the switch deck is the rotor which comprises a pair of double-ended movable contact members 26 (only one of which is visible) mounted back to back on opposite sides of an insulator 28 by a pair of rivets 3b. The insulator 28 is suitably apertured at its center to cooperate with the flatted lower end of operating shaft d whereby the rotor may be driven by the operating shaft. The circuit-making ends of the movable contact members bear at opposite sides of the stationary contact segments 22 and 2 5 and are sprung slightly apart thereby to provide good electrical conducting engagement between the members.

Each of the stationary contacts 22 and 24 have portions extending through the wall of stator housing 20 to provide external terminal portions 22a and 24a, respectively. It is also to be noted that narrow tabs 32 project inwardly from the wall of housing 20 in the spaces between adjacent stationary contacts. These tabs 32 are formed of the same material as the stationary contacts 22 and 24 but are electrically isolated from the stationary contact portions within the molded wall portion of housing 2%. Tabs 32 serve to maintain the ends of contacts 26 apart for nonshorting action when the latter move between stationary contact segments and also provide a nonconducting scraping surface for cleaning the movable contacts as they pass thereover.

In the operation of a switch, electrical arcing occurs most commonly and most severely upon contact separation. The amount of arcing is directly proportional to the amount of current that the switch is required to carry; the greater the current, the more severe the arcing. Switches of the aforedescribed type are presently available to operate at v. AC and interrupt 1 ampere repeatedly with little or no harmful arcing.

When the rotary switch disclosed in the drawings is operated, an arc may be formed between the leading edge of the movable contact 26 and the forward edge of a stationary contact segment 24 just before the movable contact closes thereon, but especially in DC applications a far more severe arc will form as the trailing edge of the movable contact 26 leaves the rear edge of a stationary contact 24. The are creates a residue which includes carbon and metallic particles emitted .in all directions therefrom, certain of these particles being directed toward and deposited upon the vertical interior wall of housing 2%) from which the contact segments project. The amount of residue emitted depends upon the strength of the arc. Since the arcing occurs at the edges of the stationary contacts, the greatest concentration of deposits formed along the housing wall is in the area between adjacent stationary contact segments 2d. Repeated arcs eventually cause a continuous deposit to be formed on the wall to conductively bridge adjacent stationary contact segments 24 and create a short circuit therebetween, thereby ending the operative life of the switch. Consequently, the greater the current value subjected upon the same switch, the shorter the operating life thereof.

In accordance with the terms of this invention, an arc shield 34 is provided which may readily be incorporated with the stator to provide a switch of improved structure that will successfully permit repeated interruptions of current at values approximately double its normal designed rating. The are shield 3 5 is shown separately in FlG. 5 and can be seen to consist of a molded ring, the external diameter of which is dimensioned to fit snuggly within the interior of stator housing 20. A plurality of upstanding generally rectangular pads 35 are formed at spaced, intervals on the ring. A majority of the pads 36 are additionally provided with pairs of upstanding projections 33 which are formed adjacent the inner corners of the pads 36 as best seen in the enlarged view of FIG. 3. Still referring to FIG. 3, it can be seen that the pads 36 having the projections 38 formed thereon are spaced to be positioned directly over the tabs 32 while those pads 36 not having the projections 38 thereon are disposed over the common contact segment 22. it may further be seen that the projections 3% lie adjacent the opposite edges of tabs 32, but are spaced away from the stationary contact segments 22 or 24. By forming theprojections I 38 at the inner comers of the pads 36, the projections 38 are also spaced away from the vertical interior wall of the stator housing 20. As can be seen in PEG. 4, the main ring portion of arc shield 34 is spaced off the stationary contact segments 22 and 24 by the pads 36 which rest upon the tabs 32 and the common contact segment 22.

With the arc shield 34 inserted in the switch deck 3 of switch 2, some of the arc residue particles emitted during switch operation are intercepted by the projections 38 and deposited thereon to prevent those particles from being deposited upon the surface of the housing wall behind the projections 38. Certain other of the carbon and metallic residue particles emitted are deflected off the projections 38 because of the cylindrical shape of the projections to permit the latter to control the arc residue deposit on a wider portion of the housing wall. Each projection 38 provides a clean area on the housing wall between adjacent stationary contact segments to thereby create a break in the short-circuiting path that would normally be formed upon the wall ,by the arc deposits, and each pair of projections 38 accordingly provide a double break in the would-be short circuit path While but a single embodiment has been disclosed herein, it is to be understood that this invention is susceptible to various modifications without departing from the scope of the appended claims.

lclaim:

1. In an electrical switch having a housing,stationary contacts mounted in said housing, and a movable contact assemblyoperable to electrically bridge pairs of said stationary contacts, the improvement comprising a member positioned between adjacent stationary contacts in spaced relation thereto and spaced away from a wall of said housing common to said adjacent stationary contacts to intercept residue particles emitted toward said wall from an are drawn between the movable and stationary contacts during a switch operation, said member thereby establishing a silhouette of itself which is free of deposited arc residue on said wall between adjacent stationary contacts,

2. The combination according to claim ll wherein said member is formed of an electrically insulating material.

3. The combination according to claim 2 wherein said member is an integral projecting portion of an insulating structureformed complementally to the interior of said switch housing, said member being maintained in position between said adjacent stationary contacts by the cooperative engagement of said structure with portions in said housing.

4. The combination according to claim 3 wherein said switch is a rotary switch having the stationary contacts thereof arranged in a circular fashion about a central axis and said movable contact is rotatable about said axis, one of said sta tionary contacts being a substantially semicircular segment which is electrically engaged by said movable contact at every position thereof and wherein said insulating structure includes a plurality ,of said members formed at spaced intervals there along to have one of said members positioned between each adjacent pair of stationary contacts.

5. The combination according to claim 4 wherein said stationary contacts project inwardly from a cylindrical interior wall of said housing, said insulating structure is ring shaped and disposed within said housing at one side of said stationary contact arrangement, and wherein said plurality of said members extend from said ring generally parallel with said cylindrical wall to the opposite side of said stationary contact arrangement.

6. An electrical switch comprising, in combination: an insulating housing;

stationary contacts mounted in said housing;

movable contact means positioned in said housing;

switch operating means connected with said movable contact means and extending externally of said housing, said operating means being operable to cause said movable contact means to electrically bridge selected pairs of said stationary contacts; and arc shield means lS said housing extending between ad acent stationary contacts in spaced relation thereto, said are shield means also being spaced from the internal wall of said housing to intercept arc residue particles emitted toward said wall upon contact operation of said switch, thereby preventing said particles from forming a continuous conductive path along the wall of said housing between adjacent stationary contacts. 7. Means for preventing a continuous deposit of electrically conductive arc residue along an interior wall of an electrical switch housing between adjacent stationary contacts extending from said wall comprising a member positioned between said adjacent stationary contacts in spaced relation thereto and spaced away from said well to intercept arc residue emitted toward said wall during contact operation of said switch to thereby establish at least one portion on said wall behind said member and between said adjacent stationary contacts which is free of deposits of said electrically conductive arc residue.

8. An electrical switch comprising, in combination: an insulating housing having a cylindrical switch cavity therein; 1

a plurality of stationary contacts mounted in said housing and extending inwardly of said cylindrical cavity, said stationary contacts forming a circular arrangement substantially concentric with said cavity; a

movable contact means rotatable to electrically bridge pairs of said stationary contacts;

external operating means mounted on said switch housing and having connection with said movable contact means to effect rotation thereof; and

an electrically insulating ring member positioned within said cavity at one side of said circular stationary contact arrangement, said ring member having a plurality of projections formed thereon to extend between adjacent stationary contacts to the other side of said stationary contact arrangement, said projections being in spaced relationship with said stationary contacts and with the wall of said cylindrical cavity.

9. The combination according to claim 8 wherein said stationary contacts include one substantially semicircular contact segment, together with:

means projecting from the cylindrical wall of said cavity between adjacent stationary contacts and being coplanar therewith; and

a plurality of spaced raised pads formed on said ring member to rest upon said substantially semicircular contact segment and on said means projecting from said wall to space said ring member 01? the remaining stationary contacts.

10. The combination according to claim 9 wherein said plurality of projections formed on said ring comprise pairs of projections formed to extend between adjacent stationary contacts and on opposite sides of said means projecting from said wall. 

1. In an electrical switch having a housing, stationary contacts mounted in said housing, and a movable contact assembly operable to electrically bridge pairs of said stationary contacts, the improvement comprising a member positioned between adjacent stationary contacts in spaced relation thereto and spaced away from a wall of said housing common to said adjacent stationary contacts to intercept residue particles emitted toward said wall from an arc drawn between the movable and stationary contacts during a switch operation, said member thereby establishing a silhouette of itself which is free of deposited arc residue on said wall between adjacent stationary contacts.
 2. The combination according to claim 1 wherein said member is formed of an electrically insulating material.
 3. The combination according to claim 2 wherein said member is an integral projecting portion of an insulating structure formed complementally to the interior of said switch housing, said member being maintained in position between said adjacent stationary contacts by the cooperative engagement of said structure with portions in said housing.
 4. The combination according to claim 3 wherein said switch is a rotary switch having the stationary contacts thereof arranged in a circular fashion about a central axis and said movable contact is rotatable about said axis, one of said stationary contacts being a substantially semicircular segment which is electrically engaged by said movable contact at every position thereof and wherein said insulating structure includes a plurality of said members formed at spaced intervals therealong to have one of said members positioned between each adjacent pair of stationary contacts.
 5. The combination according to claim 4 wherein said stationary contacts project inwardly from a cylindrical interior wall of said housing, said insulating structure is ring shaped and disposed within said housing at one side of said stationary contact arrangement, and wherein said plurality of said members extend from said ring generally parallel with said cylindrical wall to the opposite side of said stationary contact arrangement.
 6. An electrical switch comprising, in combination: an insulating housing; stationary contacts mounted in said housing; movable contact means positioned in said housing; switch operating means connected with said movable contact means and extending externally of said housing, said operating means being operable to cause said movable contact means to electrically bridge selected pairs of said stationary contacts; and arc shield means is said housing extending between adjacent stationary contacts in spaced relation thereto, said arc shield means also being spaced from the internal wall of said housing to intercept arc residue particles emitted toward said wall upon contact operation of said switch, thereby preventing said particles from forming a continuous conductive path along the wall of said housing between adjacent stationary contacts.
 7. Means for preventing a continuous deposit of electrically conductive arc residue along an interior wall of an electrical switch housing between adjacent stationary contacts extending from said wall comprising a member positioned between said adjacent stationary contacts in spaced relation thereto and spaced away from said wall to intercept arc residue emitted toward said wall during contact operation of said switch to thereby establish at least one portion on said wall behind said member and between said adjacent stationary contacts which is free of deposits of said electrically conductive arc residue.
 8. An electrical switch comprising, in combination: an insulating housing having a cylindrical switch cavity therein; a plurality of stationary contacts mounted in said housing and extending inwardly of said cylindrical cavity, said stationary contacts forming a circular arrangement substantially concentric with said cavity; movable contact means rotatable to electrically bridge pairs of said stationary contacts; external operating means mounted on said switch housing and having connection with said movable contact means to effect rotation thereof; and an electrically insulating ring member positioned within said cavity at one side of said circular stationary contact arrangement, said ring member having a plurality of projections formed thereon to extend between adjacent stationary contacts to the other side of said stationary contact arrangement, said projections being in spaced relationship with said stationary contacts and with the wall of said cylindrical cavity.
 9. The combination according to claim 8 wherein said stationary contacts include one substantially semicircular contact segment, together with: means projecting from the cylindrical wall of said cavity between adjacent stationary contacts and being coplanar therewith; and a plurality of spaced raised pads formed on said ring member to rest upon said substantially semicircular contact segment and on said means projecting from said wall to space said ring member off the remaining stationary contacts.
 10. The combination according to claim 9 wherein said plurality of projections formed on said ring comprise pairs of projections formed to extend between adjacent stationary contacts and on opposite sides of said means pRojecting from said wall. 